Image processing method and image processing apparatus

Abstract

An image processing method of performing filtering on image blocks using a plurality of deblocking filters having different filter strengths includes: a first parameter calculating step of calculating a first parameter indicating a boundary strength; a second parameter calculating step of calculating a second parameter indicating a limit value for each of the deblocking filters, based on the first parameter and a quantization parameter; and a selecting step of selecting a deblocking filter to be used in the filtering from among the deblocking filters, using one or more threshold values which are determined based on the second parameter.

The invention claimed is: 
     
       1. An image decoding method involving filtering of two adjacent transform units using at least one of a plurality of deblocking filters having different filtering widths, the image decoding method comprising:
 determining whether or not a deblocking filter is to be applied to the two adjacent transform units based on a result of whether or not a first value is larger than a predetermined value, the first value being determined based on whether or not an absolute difference in pixel values between pixels in the two adjacent transform units is larger than a predetermined threshold value; 
 selecting a deblocking filter to be used in the filtering from among the plurality of deblocking filters, when a deblocking filter is determined to be applied to the two adjacent transform units in said determining; and 
 applying the selected deblocking filter on adjacent edges of the two adjacent transform units, 
 wherein the selecting includes: 
 determining, by using pixels in a first width, whether or not a first deblocking filter from among the plurality of deblocking filters is selected, the first width being from a boundary between the two adjacent transform units in the two adjacent transform units; and 
 determining, by using pixels in a second width which is different from the first width, when the first deblocking filter is determined not to be selected by using the pixels in the first width, whether or not a second deblocking filter from among the plurality of deblocking filters is selected, the second deblocking filter having a different filtering width than the first deblocking filter, the second width being from the boundary between the two adjacent transform units in the two adjacent transform units. 
 
     
     
       2. The image decoding method according to  claim 1 , wherein no deblocking filter is selected when the first deblocking filter and the second deblocking filter are not selected. 
     
     
       3. An image decoding apparatus which performs decoding involving filtering of two adjacent transform units using at least one of a plurality of deblocking filters having different filtering widths, the image decoding apparatus comprising:
 a determining unit configured to determine whether or not a deblocking filter is to be applied to the two adjacent transform units based on a result of whether or not a first value is larger than a predetermined value, the first value being determined based on whether or not an absolute difference in pixel values between pixels in the two adjacent transform units is larger than a predetermined threshold value; 
 a selecting unit configured to select a deblocking filter to be used in the filtering from among the plurality of deblocking filters, when the determining unit determines that a deblocking filter is to be applied to the two adjacent transform units; and 
 an applying unit configured to apply the selected deblocking filter on adjacent edges of the two adjacent transform units, 
 wherein the selecting unit is configured to: 
 determine, by using pixels in a first width, whether or not a first deblocking filter from among the plurality of deblocking filters is selected, the first width being from a boundary between the two adjacent transform units in the two adjacent transform units; and 
 determine, by using pixels in a second width which is different from the first width, when the first deblocking filter is determined not to be selected by using the pixels in the first width, whether or not a second deblocking filter from among the plurality of deblocking filters is selected, the second deblocking filter having a different filtering width than the first deblocking filter, the second width being from the boundary between the two adjacent transform units in the two adjacent transform units. 
 
     
     
       4. The image decoding apparatus according to  claim 3 , wherein no deblocking filter is selected when the first deblocking filter and the second deblocking filter are not selected. 
     
     
       5. An image decoding apparatus which performs decoding involving filtering of two adjacent transform units using at least one of a plurality of deblocking filters having different filtering widths, the image decoding apparatus comprising:
 at least one processor; and 
 storage accessible by the at least one processor; 
 the at least one processor executing the following steps using the storage: 
 determining whether or not a deblocking filter is to be applied to the two adjacent transform units based on a result of whether or not a first value is larger than a predetermined value, the first value being determined based on whether or not an absolute difference in pixel values between pixels in the two adjacent transform units is larger than a predetermined threshold value; 
 selecting a deblocking filter to be used in the filtering from among the plurality of deblocking filters, when a deblocking filter is determined to be applied to the two adjacent transform units in said determining; and 
 applying the selected deblocking filter on adjacent edges of the two adjacent transform units, 
 wherein the selecting includes: 
 determining, by using pixels in a first width, whether or not a first deblocking filter from among the plurality of deblocking filters is selected, the first width being from a boundary between the two adjacent transform units in the two adjacent transform units; and 
 determining, by using pixels in a second width which is different from the first width, when the first deblocking filter is determined not to be selected by using the pixels in the first width, whether or not a second deblocking filter from among the plurality of deblocking filters is selected, the second deblocking filter having a different filtering width than the first deblocking filter, the second width being from the boundary between the two adjacent transform units in the two adjacent transform units. 
 
     
     
       6. The image decoding apparatus according to  claim 5 , wherein no deblocking filter is selected when the first deblocking filter and the second deblocking filter are not selected. 
     
     
       7. An image decoding method involving filtering of two adjacent transform units using at least one of a plurality of deblocking filters having different filtering widths, the image decoding method comprising:
 determining whether or not a deblocking filter is to be applied to the two adjacent transform units; 
 selecting a deblocking filter to be used in the filtering from among the plurality of deblocking filters, when a deblocking filter is determined to be applied to the two adjacent transform units in said determining; and 
 applying the selected deblocking filter on adjacent edges of the two adjacent transform units, 
 wherein the selecting includes: 
 determining, by using pixels in a first width, whether or not a first deblocking filter from among the plurality of deblocking filters is selected, the first width being from a boundary between the two adjacent transform units in the two adjacent transform units; and 
 determining, by using pixels in a second width which is different from the first width, when the first deblocking filter is determined not to be selected by using the pixels in the first width, whether or not a second deblocking filter from among the plurality of deblocking filters is selected, the second deblocking filter having a different filtering width than the first deblocking filter, the second width being from the boundary between the two adjacent transform units in the two adjacent transform units.